Fluid energy machines, in particular turbocompressors, are often sealed at the shaft ends of a rotor by dry gas seals of tandem design (tandem dry gas seals) in order to prevent process gas that is to be compressed from escaping into the environment via the shaft gaps. These dry gas seals must be supplied with dry and filtered sealing gas in order to avoid contaminants and moisture, which prejudice the functioning of the seal. For reliable and stable operation, a pressure is required in the interspace between the inner seal and the outer seal, and this must also be monitored. Only if a pressure gradient is established in this way in the outer gas seal is monitoring of functioning on the outer gas seal possible. More particularly, this pressure gradient across the outer gas seal is also required in order to avoid overheating and instabilities in the gas film between a slip ring and a rotating ring of this seal.
Corresponding arrangements having dry gas seals on fluid energy machines, in particular turbocompressors, are already known from documents WO 2010/034601 A1, WO 2010/034605 A1, WO 2010/102940 A1, WO 2010/118977 A1 and WO 2014/037149 A1. In particular, WO 2010/034601 A1 has already disclosed the problem of monitoring the outer dry gas seal because a low pressure gradient across the outer dry gas seal may occur owing to the low leakage, especially in operating states that do not correspond to full load. In this context, the leakage of the inner dry gas seal is sometimes so low that the pressure in the interspace between the inner dry gas seal and the outer dry gas seal drops. Another problem is the lack of a supply of a cooling fluid to the outer dry gas seal, in particular a process fluid exerting pressure from the inside of the outer dry gas seal or a mixture with the process fluid, ensuring the lubrication and cooling of this seal. To counteract this problem, it is possible to feed relatively large quantities of sealing fluid into the interspace or into the seal itself, thus ensuring cooling and lubrication. However, this has the additional disadvantage that a relatively large quantity of sealing fluid is required, the preparation and provision of which is very expensive and may even prejudice the efficiency of the machine.